Chestnut Blight in Southern Switzerland: Influence of Hypovirulence and Management Practice

In Switzerland, the main chestnut (Castanea sativa) growing areas are located south of the Alps. There, chestnut is the dominant tree species of the colline region, covering over 15,000 ha. The European chestnut south of the Alps has been exposed to chestnut blight (Cryphonecma parasitica) for over 40 yr. The survival of C. sativa is due primarily to its reduced susceptibility toward C. parasitica compared with C. dentata, and to the appearance of hypovirulent strains of the fungus. During 1988, an investigation to verify the distribution and the severity of the disease in southern Switzerland was undertaken. The field observations confirmed the wide distribution of the disease and showed the predominance of superficial cankers (probably due to hypovirulence) in all of the areas investigated. The disease situation in a particular forest stand seems to be more dependent on management practice and management intensity rather than on site conditions. Due to the presence of only a few vegetative compatibility groups of the fungus together with the fact that the chestnut stands are mostly mature and not under active silvicultural management, the disease situation has improved. There is evidence for the presence of substantial inoculum of virulent strains of C. parasitica, which could be an obstacle to intensify chestnut cultivation. Presently, there does not seem to be any danger for the survival of the species south of the Alps. Chestnut fruit groves can be revived and improved, provided all the necessary healthmaintaining interventions characterizing modern chestnut cultivation are undertaken.

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Author(s): Marco Conedera, Ursula Heiniger

Publication: American Chestnut Proceedings - 1992